The long-term effects of methylphenidate on hyperkinetic children will be closely monitored in a group of adolescents and young adults 5 to 15 years after first administration of the psychotropic drug. Extensive interviewing of the person and his/her parents will be conducted at age 16 in comparison with cohort adolescents of the same age. Attention deficit disorders in hyperkinetic children will be systematically studied using a variety of laboratory tasks and classroom tasks in an attempt to assess the distractibility and inattentiveness of the children and the effects of stimulant medication alone and in conjunction with behavioral and cognitive therapies. The relationship between performance on attention tasks and psychophysiological indices of arousal as indicated by the heart rate and heart rate variance will be investigated. An attempt will be made to develop a teacher rating scale based primarily on the Conners' Rating Scales in order to differentiate attention deficit disorders, hyperkinesis, and conduct problems in children. The ratings will be validated with extensive observation in the classroom, attention measures from the laboratoy, psychophysiological measures, and performance on achievement tests.